Solar cells are devices that convert the energy of light into electricity using the photovoltaic effect. Solar power is an attractive green energy source because it is sustainable and produces only non-polluting by-products. Accordingly, a great deal of research is currently being devoted to developing solar cells with enhanced efficiency while continuously lowering material and manufacturing costs. In operation, when light hits a solar cell, a fraction of the incident light is reflected by the surface and the remainder is transmitted into the solar cell. The photons of the transmitted light are absorbed by the solar cell, which is usually made of a semiconducting material such as silicon. The energy from the absorbed photons excites electrons of the semiconducting material from their atoms, generating electron-hole pairs. These electron-hole pairs are then separated by p-n junctions and collected by conductive electrodes applied on the solar cell surface.
Solar cells typically have electroconductive pastes applied to both their front and back surfaces. A front side paste, which typically includes silver, is screen printed onto the front side of the substrate to serve as a front electrode. A typical electroconductive paste contains conductive metallic particles, glass frit, and an organic vehicle. In some instances, the glass frit etches through an antireflection coating, such as a silicon nitride coating, on the surface of the silicon substrate upon firing, helping to build electrical contact between the conductive particles and the silicon substrate. On the other hand, it is desirable that the glass frit is not so aggressive that it shunts the p-n junction after firing. For example, glass frits which include relatively high amounts of lead oxide and bismuth oxide may damage the antireflection layer and degrade the p-n junction of the substrate. As a result, the electrical performance of the solar cell may be reduced. In addition, glass frits are known to have wide melting temperature ranges, making their behavior strongly dependent on their composition and processing parameters. As such, the ability to predict glass processing parameters and behavior under fast firing processes is difficult with known glass frits.
Thus, an IRS which optimizes contact between the electroconductive paste and the underlying substrate so as to achieve improved solar cell efficiency, without being so aggressive that it damages the antireflection layer and p-n junction, is needed. Further, an IRS having more predictable processing behaviors is also desirable.